Kinetics of Thrombin Inactivation as Influenced by Physical Conditions, Trypsin, and Serum

1. A new technique for studying the progressive inactivation of thrombin is described. 2. Thrombin inactivation follows the kinetics of a first order reaction. 3. The rate constant of the inactivation reaction increases with temperature and pH (5.0 --> 10.0), and also with the presence of crystalline trypsin, or serum. The rate varies for different thrombin preparations, even under the same experimental conditions. 4. The temperature characteristics of the reaction indicate that thrombin is associated with protein. 5. Thrombin preparations are most stable at pH 4 to 5, even when trypsin or serum is added. 6. The progressive inactivation is believed to be due to two mechanisms: (1) a major effect, thought to be the action of a "serum-tryptase," which is usually present in the thrombin preparations, and (2) a minor effect, probably attributable to denaturation of thrombin-protein. 7. Sources of the thrombinolytic factor (serum-tryptase) and its implications in the general theory and practical problems of blood coagulation and antithrombic action are briefly discussed.